I use healthy oils for baking. I also replace oil for butter. If you want though you can substitute oil by using: applesauce, fruit puree or yogurt. I have used applesauce. If you make brownies and add applesauce instead of oil your kids might complain, mine did.
If you don't have buttermilk you can make your own but adding 1 Tablespoon of either fresh lemon juice or vinegar to a cup of milk. I have made it using the vinegar.
Out of eggs? Use any of these substitutes in place of 1 egg: 1/4 cup applesauce or 1/4 cup vegetable oil or 1/4 cup mashed banana.
Cut a recipe in half:
3/4 cup is 6 Tablespoons - 2/3 cup is 1/3 cup - 1/2 cup is 1/4 cup - 1/3 cup is 2 teaspoons plus 2 Tablespoons - 1/4 cup is 2 Tablespoons - 1 Tablespoon is 1 1/2 teaspoons - 1 teaspoon is 1/2 teaspoon - 1/2 teaspoon is 1/4 teaspoon.
Heavy Cream Substitute
If you need heavy cream for a recipe, make your own by combining 2/3 cup whole milk with 1/3 cup melted unsalted butter. This will give you 1 cup of heavy cream. (I normally don't use unsalted butter and recipes that call for it I just use salted butter.)
Maple syrup instead of corn syrup.